The invention relates to implantable articles and methods for implanting such articles. More particularly, the invention relates to a bone prosthesis and a method for implanting the same.
There are known to exist many designs for and methods of implanting implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints, such as elbows, hips, knees and shoulders.
Early designs of implantable articles relied upon the use of cements to anchor the implant. However, the current trend is to use cements to a lesser extent because of their tendency to lose adhesive properties over time and the possibility that cement contributes to wear debris within a joint.
Recently, implantable bone prostheses have been designed such that they encourage the growth of hard bone tissue around the implant. Such implants are often implanted without cement and the bone grows around surface irregularities, for example, porous structures on the implant.
One such implantable prosthesis is a shoulder prosthesis. During the lifetime of a patient it may be necessary to perform a total shoulder replacement procedure on a patient as a result of, for example, disease or trauma, for example, disease from osteoarthritis or rheumatoid arthritis. Currently, most implantable shoulder prostheses are total shoulder prostheses. In a total shoulder replacement procedure, a humeral component having a head portion is utilized to replace the natural head portion of the upper arm bone or humerus. The humeral component typically has an elongated intramedullary stem, which is utilized to secure the humeral component to the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface for the head portion of the humeral component.
With the average age of patients requiring shoulder arthroplasty decreasing, device manufacturers are developing bone sparing implants for the initial treatment of degenerative arthritis. Surface replacement prostheses are being developed to replace the articulating surface of the proximal humerus with a minimal bone resection and minimal disruption of the metaphysis and diaphysis. Current designs utilize a semi-spherical articular dome with a small stem for rotational stability. The under surface of the articular head is also semi-spherical and mates with the spherically machined humeral head.
The need for a shoulder replacement procedure may be created by the presence of one of a number of conditions. One such condition is the deterioration of the patient's rotator cuff. Specifically, an intact rotator cuff stabilizes the humeral head in the glenoid fossa of a scapula during abduction of the arm. While it is stabilized in such a manner abduction of the arm causes the humeral head to translate only a short distance in the superior direction (e.g. a few millimeters), whereby a space is maintained between the humeral head and the acromion. However, for patients with rotator cuff arthropathy, significantly greater humeral excursion is observed.
Referring to FIG. 2, a healthy long bone in the form of humerus 1 is shown. The humerus 1 includes a healthy humeral head 2.
Referring now to FIG. 3, a diseased humerus 3 is shown. The diseased humerus 3 includes a diseased or flattened humeral head 4. Whereas the healthy humeral head 2 of the healthy humerus 1 of FIG. 2 has a generally hemispherical shape, the flattened humeral head 4 is quite flat and only slightly domed.
Referring now to FIGS. 4, 5 and 6, a prior art prosthesis 5 is shown. Referring first to FIG. 4, the prosthesis 5 is shown installed on the diseased humerus 3. The prosthesis 5 is positioned over flattened head or bony defect 4. The prosthesis 5 includes a hollow generally hemispherical cup 6. Extending distally from the interior of the cup 6 is a generally conically shaped stem 15 that anchors the prosthesis 5 into the humerus 3.
Referring now to FIGS. 5 and 6, the prosthesis 5 is shown implanted in a shoulder joint. As shown in FIG. 5, the humerus 3 is shown in a position in which the arm is resting against the patient's torso. Articulating surface of the cup 6 of the prosthesis 5 is shown in contact with the scapula 7, the clavicle 8, and the acromion 9. As can be seen in FIG. 5, in this downward position of the humerus 3 the prosthesis 5 provides the articulating surface of cup 6 in contact with the acromion 9, the clavicle 8, and the scapula 7 to provide for a acceptable artificial joint in this position.
However, referring to FIG. 6, the humerus 3 is shown abducted in the direction of arrow 10 such that the long bone or humeral centerline 11 is at an angle α of about fifteen (15) degrees with the vertical centerline 12. As can be seen in FIG. 6, on a slight abduction of fifteen degrees, the acromion 9 is positioned outside the articulating surface 6 of the prosthesis 5 causing the acromion 9 to impinge upon the humerus 3 causing great pain to the patient and severely limited motion of the humerus 3.
In particular, hyper-translation of the humeral head in the superior direction is observed in patients with massive rotator cuff deficiency, thereby resulting in articulation between the superior surface of the humeral head and both the inferior surface of the acromion and the acromioclavicular joint during abduction of the patient's arm. Such articulation between these components accelerates humeral articular destruction and the erosion of the acromion and acromioclavicular joint. Moreover, such bone-to-bone contact is extremely painful for the patient, thereby significantly limiting the patient's range of motion. In short, patients with massive rotator cuff tear and associated glenohumeral arthritis, as is seen in cuff tear arthropathy, may experience severe shoulder pain, as well as reduced function of the shoulder.
In order to treat patients suffering from cuff tear arthropathy, a number of prostheses and techniques utilizing existing prostheses have heretofore been designed. For example, surgeons heretofore utilized a relatively large humeral head prosthesis in an attempt to completely fill the shoulder joint space. It was believed that such use of a large prosthesis would increase the efficiency of the deltoid muscle, thereby improving motion of the shoulder. However, clinical experience has shown that such use of a large humeral head prosthesis (overstuffs) the shoulder joint thereby increasing soft tissue tension, reducing joint range of motion, and increasing shoulder pain. Moreover, such use of an oversized prosthetic head fails to resurface the area of the greater tubercle of the humerus, thereby allowing for bone-to-bone contact between the greater tubercle and the acromion during abduction of the patient's arm.
A number of humeral head bipolar prostheses have also been utilized in an attempt to address the problems associated with cuff tear arthropathy. It was believed that the relatively unstrained motion of the bipolar head would improve shoulder motion. However, heretofore designed bipolar prosthetic heads include relatively large offsets, thereby overstuffing the shoulder joint in a similar manner as described above. Moreover, scar tissue may form around the bipolar head thereby (freezing) the dual articulating motion of the prosthesis that has been known to create a large hemi arthroplasty that likewise overstuffs the shoulder joint. In addition, such bipolar prosthetic heads do not cover the articulating surface between the greater tubercle and the acromion, thereby creating painful bone-to-bone contact between them.
Yet further, a number of techniques have heretofore been designed in which the relatively rough surface of the greater tubercle is resurfaced with an osteotome or high speed burr. Although this approach results in a smoother tubercle contact surface, relatively painful bone-to-bone articulating contact still occurs, thereby reducing the patient's range of motion.
More recently, the assignee of the applicant of the present invention has invented a method and apparatus for performing a shoulder replacement procedure in a treatment of a cuff tear arthroplasty which has been filed in the U.S. Patent and Trademark Office under U.S. application Ser. No. 09/767,473 filed Jan. 23, 2001, hereby incorporated in its entireties by reference in this application. This application provides for a method and apparatus for treating cuff tear arthroplasty utilizing a total shoulder replacement prosthesis. This prosthesis includes an artificial head as well as a stem that extends into a rimmed medullary canal. Such a prosthesis is limited to use with a total shoulder prosthesis and is not suitable for use with bone sparing implants for the initial treatment of the degenerative arthritis.
What is needed, therefore, is a method and apparatus for performing bone sparing arthroplasty shoulder replacement surgery utilizing bone sparing implants for the initial treatment of degenerative arthritis, which will be useful in the treatment of cuff tear arthroplasty, which overcomes one or more of the aforementioned drawbacks. What is particularly-needed is a method and apparatus for performing a bone sparing implant shoulder procedure that eliminates painful articulation between the great tubercle of the humerus and the acromion.